There are two major main concerns about the use of mobile or portable radiographic x-ray equipment, radiation safety and image quality. These concerns should dictate that the use of mobile equipment be restricted to patients who, for medical reasons, cannot be transported to a stationary machine. While sometimes necessary for patient care, mobile exams should not be performed either for the sake for convenience or for lack of transport personnel. It is important for radiologists, technologists, and administrators to understand these concerns to see that mobile examinations are properly ordered. Stationary or permanently installed radiography systems are required to be shielded. A shielding calculation is performed by a medical physicist for each room barrier including the ceiling and floor. This calculation takes into account the anticipated workload, the type of examinations performed, distances from the source of radiation to each barrier, and the anticipated occupancy behind each barrier. Shielding designs are required to be approved by the governmental regulatory agency and must be checked for both integrity and adequacy during installation. Shielding a stationary x-ray room is a time-consuming and expensive process done to ensure individuals in the immediate area are properly protected. No such protection is available when mobile equipment is used, potentially exposing nearby staff and other members of the public. Thus radiographs should be obtained using stationary x-ray units whenever possible. A second concern in the use of mobile equipment for radiography is image quality. Source to image distance can be difficult to measure and alignment of the x-ray tube and receptor must be done manually. Accurate and consistent geometry is important to image quality. A properly installed stationary radiographic unit provides tools to assist the radiographer in achieving consistent geometry. It is difficult to achieve the same level of consistency using mobile equipment because such alignment tools are generally not available. Improper geometry affects image quality in several ways. Because of the inverse square law, small deviations in source to image distance can result in substantial changes to the amount of radiation reaching the image receptor. Misalignment of the x-ray tube to the image receptor can cause both distortion and artifacts associated with the grid, which can affect the appearance of the image as well as the amount of radiation reaching the receptor. The following links describe the importance of Tube / Image Receptor Alignment: |